Combined steam and gas turbine plants have been proposed for many different applications, the usual advantage being utilizing the residual heat from the gas turbine as a heat input to the steam generator of the steam turbine, thereby improving total efficiency and economy. Further, the fluidized bed combustion chamber has proved to possess qualities which make it advantageous for gas turbine operation. However, for direct steam generation by placing a steam generator coil in the fluidized bed to produce steam for turbine operation, the fluidized bed combustion chamber has proved to be less suitable than more conventional boilers, due to the difficulty in regulating the load in the fluidized bed during periods of low demand on the steam turbine.